foods easy on the kidneys?

speedy loves all the different foods he eats, but they are higher in protein, and he's older...it's harder on the kidneys. they aren't functioning like they did when he was younger, and i want to feed him something that may be easier on them, but he is picky, so it would have to be something that tastes good to him! also, i will not feed any hills foods, we fed CD to a cat a long time ago, the poops were STANK, and a LOT, and the coat looked horrible. i'm just trying to find out what is out there, in the high quality foods. right now they are eating eagle pack chicken and rice dry, and they eat canned merrick,eagle pack, EVO, and a few other holistic brands. any ideas, i would really appreciate! thanks!